1. Field of the Invention
This invention relates to a shock absorber device for preventing breakage of cables and the like resulting from the application of impact loads, and more particularly to a shock absorber adapted to be connected with a morring cable that is, in turn, connected with a vessel that is moored to a dock, or a cable that connects a towing vessel and a towed vessel.
2. Description of the Related Art
Marine vessels are typically moored to a dock or to some fixed object rigidly positioned on a shoreline or on a shore-based structure by means of heavy cables that are intended to withstand the tensile loads that result when the vessel is drawn in a downstream direction by virtue of the flow of a current or the action of waves from passing vessels. In the case of heavy vessels, such as groups of barges that are interconnected to be pushed along a river as a barge fleet by a tow boat, when the barge fleet is moored to the bank, the mooring cables, which oftentimes are large diameter steel cables, have a tendency to break when high loads are applied suddenly, as sometimes results when a riverboat passes close by. Under such conditions, the passing boat causes wave action that, in turn, sometimes causes the moored barge fleet to move upriver for a short distance, against the flow of the current. As a result, the mooring cables become slack, and after the passing riverboat is far enough away, and the effects of its passage have dissipated, the flowing current carries the barge fleet along with it.
When the movement of the fleet in a downstream direction has been sufficient to take up the slack in the mooring cable there is a sudden application of a very high tensile load in the mooring cable caused by the cable having to withstand and absorb the impact load resulting from the momentum of the moving barge fleet. Depending upon the weight of the barges and their contents, and also dependent upon the velocity of the fleet of barges, the sudden application of a high tensile load to the mooring cables frequently causes the cables to break, resulting in the fleet of barges being carried downstream in an uncontrolled manner, possibly causing damage when the barges collide with other barges or vessels that might be moored nearby on the downstream side. Additionally, even if the mooring cables do not initially break, repeated application of such impact loads gradually stretches and weakens the cables so that ultimately a failure occurs.
Various types of shock absorber structures have been suggested in the past for absorbing shock loads in anchor cables, but those devices have been intended for use with small vessels, and not with large fleets of interconnected barges. For example, in U.S. Pat. No. 593,788, which issued Nov. 16, 1897, to J.B. Stone, there is disclosed a shock absorber in the form of a pair of coaxial springs that are positioned within a sealed housing that contains oil, the flow of which is controlled by the size of apertures formed in a piston-type head to resist and limit the rate of travel of the spring assembly and thereby absorb shock loads.
Examples of other shock absorber constructions adapted for nautical use are shown in U.S. Pat. No. 608,344, which issued Aug. 2, 1898, to F.P. Nesmith; U.S. Pat. No. 869,130, which issued Oct. 22, 1907, to F.A. Bierie; and U.S. Pat. No. 4,754.957, which issued Jul. 5, 1988, to V.H. Muttart. However,p in each case, the shock absorbers disclosed in those patents are intended for small vessels, and would be unsatisfactory for use with heavy fleets of barges, which generate very high impact loads in mooring cables.
Accordingly, it is an object of the present invention to provide an improved shock absorber structure for use with mooring cables for heavy vessels, in order to avoid the imposition on the cables of sudden impact loads that would otherwise break the mooring cables.